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Cold Slug

Cold slug material flow marks are caused when molten plastic passes through a gate or nozzle, solidifies slightly in advance, and enters the cavity along with the molten plastic in the rear section. The situation is as serious as the non-profound combination line.

Dull Spots Near The Spurs

This defect is actually high shear stress cracking, mostly in the submerged gate and plastic parts with high viscosity. When the high viscosity molten plastic passes through the very thin opening, it needs high speed and high pressure to pass through so that the overloading cracking defect will occur near the entrance gate.


Injection jetting mark is the plastic injection molding machine plasticization of the amount of insufficient, or the plastic in the state of incomplete melting through the gate and after the molten plastic into the cavity when the phenomenon.

Flaking Of The Surface Layer

It is the plastic formulation of the injection molding part that produces incomplete fusion after forming or the plastic formulation (including additives) that produces repulsive splitting after forming.

Entrapped Air

This is the injection part in the melting process or in the use of excessive backwire function mixed with a lot of air, and in the injection process into the mold cavity. The plastic material is transparent grade and is more easily found.

Burnt Streaks

There are several reasons for this defect. Thermal discoloration occurs when a polymer is heated too much and the chains of molecules break apart and are either thermally degraded or burned. Sometimes it’s just a yellowish discoloration or slight thermal degradation, which is not only caused by the burning of the polymer, but also by the presence of the rotator inside the polymer. If the melt does not appear a brown, yellow or black color change in the cleaning machine, it indicates that the melt begins to burn after leaving the nozzle. The main diameter, flow path, water level and mold design should be checked or injection speed and pressure should be corrected. If coffee streaks or discoloration are found in the cleaning machine, it proves that degradation occurs in the barrel and nozzle. If a stripe of coffee and argent stripe occurs at the same time, that is moisture element certainly.

Stress Crack

This defect is caused by the excessive shear stress of the plastic in the process of wang molding. Referring to the plastic under the condition of insufficient heating, flow is not good, forced to push it with greater pressure into the cavity, at this time the molecular excessive elongation aging, so that it is easy to fracture and turtle crack, transparent plastic more easily see this phenomenon.

Sink Marks

There are many reasons for this phenomenon, such as improper selection of plastic characteristics, poor plastic part design, and poor injection conditions. The main performance will be slow plastic curing, insufficient effective pressure holding time or poor pressure holding transmission.

Density Bubble

The defect is mainly caused by the insufficient density of the plastic in the injection molding process. The failure to fill the plastic parts with adequate density is related to the type of plastic (crystalline/amorphous), premature stop of the flow rate into the plastic or poor plastic parts design.


This defect is mainly caused by excessive plastic filling during the injection molding process. Plastic parts excessive filling and plastic grade (flow index MFI), plastic parts bad design, mold damage or injection molding machine type, injection molding machine efficiency and adjustment.

Scratch Marks

This phenomenon is mainly caused by excessive friction between the injection part and the wall surface and the corner of the mold during the demolding process after the injection. It is mainly related to the insufficient demoulding slope of plastic parts, the insufficient structural strength of labor mold, damage of labor mold, or the efficiency of injection molding machine and adjustment of injection molding parameters.